Valve bodies of on-off valves that control liquid fuel supplied to automobile engines and general-purpose engines include on-off valves that work in concert with a valve seat to open and close a fluid passage by causing the valve body to operate in a direction perpendicular to the closed face. In addition to being durable, these valves are required to be highly fluid tight and dimensionally precise in order to maintain engine performance.
A typical on-off valve that controls liquid fuel supplied to an engine is an inlet valve located at the inlet portion of a fixed fuel chamber to control liquid fuel sent from a fuel pump to a float-type or diaphragm-type fixed fuel chamber of an carburetor. The valve body thereof moves linearly in compliance with a lever that rotates in accordance with the rising or falling of the float or the displacement of the diaphragm, controlling the flow of the liquid fuel in concert with a valve seat provided in a fuel passage.
There are carburetors and, in particular, carburetors for small-exhaust-volume general-purpose engines handle liquid fuel at extremely low flow rates. In such cases a minor deviation in the fuel flow rate greatly affects engine performance. As a result, the fuel passage must be completely closed when the inlet valve is closed and must faithfully open in response to movement of the float or diaphragm, i.e. a drop in fuel in the fixed fuel chamber. As such, the portion forming the valve face for the valve seat of the valve body is made of an elastic polymer material with excellent oil resistance, such as fluororubber, and is made to be both durable and fluid tight with consideration going to minimizing swelling.
FIGS. 4(A) and (B) illustrate valve bodies currently used in an inlet valve of a diaphragm-type fixed-fuel chamber. The valve body shown in FIG. 4(A) comprises an injection hole 52 at the tip portion of a metal round-axle valve element 51 with axial grooves. A base portion 54 of a valve member 53 made of fluororubber fills the injection hole 52, and a forward-protruding tip portion 55 is given a conical shape. In FIG. 4(B), a short axle 58 and a conical head 59 protrude in a unitary manner from the tip of a metal round-axle valve element 57 with axial grooves similar to that noted above. A conical valve member 60 made of fluororubber is firmly joined to the head 59.
In each of the valve bodies mentioned above, the valve members 53, 60 are formed with injection molding using a metal die that forms a conical valve face. The portion to become the valve face is then polished to provide the prescribed conical shape of the apex. Extensive manufacturing equipment is required as a result.
In addition, a variety of liquid fuels such as a fuel blended to meet exhaust gas regulations or a fuel used for inspection and adjustment during the manufacture of the carburetor in addition to gasoline and ethanol-blended gasoline, which are widely known liquid fuels, flow over the periphery of the valve body for an extended period of time. The valve members 53, 60, as a result, make contact with the variety of liquid fuels for an extended period of time and unavoidably swell.
FIGS. 5(A) and (B) illustrate the conditions in the system before and after swelling when the valve body of FIG. 4(A) is used as the inlet valve of the diaphragm-type fixed fuel chamber. A base portion of the round axle unit 51 is attached to the tip of a lever 66 rotatably supported by a pin 65. The valve member 53 is brought into tight contact with a valve seat 68 and closes a fuel passage 69 under the spring force of a valve-closing spring 67 that acts on the lever 66. The base portion of the lever 66 and the central portion of the diaphragm 70 are, as shown in FIG. 5(A), adjusted so as to have a slight gap “a”.
When the volume of fuel in a fixed fuel chamber 71 drops, the diaphragm 70 is displaced toward the fixed fuel chamber 71 and rotates the lever 66 clockwise as shown in the drawing to cause the valve member 53 to separate from the valve seat 68, whereupon fuel is introduced into the fixed fuel chamber 71. When the volume of fuel in the fixed fuel chamber 71 rises, the diaphragm 70 is displaced in the opposite direction to that previously mentioned, and the lever 66 rotates counterclockwise, seating the valve member 53 on the valve seat 68. Therefore, in order for a fixed volume of fuel to be accurately provided to the fixed fuel chamber 71 and fuel to be supplied to the engine at an accurate flow rate, the gap “a” and the load characteristics of the valve-closing spring 67 must be appropriately set, and the gap “a” must be precisely adjusted.
But swelling of the valve member 53 appears as elongation in the axial direction. When the swelling of the valve member 53 shown in FIG. 5(B) results in elongation to the extent of “c” in the axial direction in comparison to the valve member 53 in FIG. 5(A) prior to swelling, the elongation “c” separates the base portion of the lever 66 from the diaphragm 70 by the lever ratio of L2:L1, which widens the gap “a to b” and compresses the valve-closing spring 67, changing its load characteristics. Therefore, the fuel passage 69 is closed to the extent of dramatically decreasing the volume of fuel in the fixed fuel chamber 71 compared to that before swelling. The fuel passage 69 is closed when a volume of fuel less than that supplied before swelling is introduced, which causes the flow rate of fuel supplied to the engine to drop and thereby negatively affects engine performance and the condition of the exhaust.
This phenomenon also occurs with the valve body shown in FIG. 4 (B). However, the impact due to swelling is larger with the valve body shown in FIG. 4(A), in which the axial length of the valve member 53 is longer than that of the valve member 60 in FIG. 4(B).
Thus, it is desirable to provide a valve body for resolving the problems associated with prior-art valve bodies comprising a valve member made of an elastic polymer material such as fluororubber and located at the tip of a valve element—i.e., manufacturing can be problematic and tend to require extensive equipment to form the valve member such as metal dies for injection molding, and thus high costs are therefore unavoidable, and axial elongation due to the swelling of the valve member directly impacts the fuel flow rate—, that can be easily manufactured without the use of a metal die and that greatly reduces the negative effect of swelling on performance during the control of the flow rate of fuel.